This application is a request for funds to provide CCD digital imaging capability for 11 major and 5 minor users of TEMs in the Core Electron Microscopy Facility of the University of Massachusetts Medical School (UMMS). Ultrastructural projects range from the tissue to the molecular level, and include low dose, tomographic, cryo-EM, serial section, immunolabeling, and morphological studies of a wide range of biomedically important systems. The major benefit of direct digital image acquisition is the instantaneous feedback that it provides, in the form of immediate images and instant knowledge of imaging parameters and specimen characteristics. These benefits make a critical difference to specialist applications, such as cryo-EM and tomography, where they can save hundreds of hours of work. In some cases studies become possible for the first time using CCD technology. The benefits of CCD imaging are also key to enhancing productivity in more routine applications. Digital acquisition not only adds convenience and saves time (by eliminating the film processing, printing, and scanning necessary for analysis and publication of images), but also results in major cost savings. In the past year, UMMS researchers spent approximately $40,000 in supplies and personnel costs for developing, printing and scanning the approximately 10,000 micrographs that were taken, all on film. Digital imaging would have eliminated almost all of these costs. Finally, digital imaging is important in teaching, facilitating instruction of novice microscopists and providing stimulating images for visiting medical, graduate and high school students. To provide for the needs of both specialist and routine TEM users alike, we are requesting funds to acquire digital imaging capability for two microscopes. These microscopes perform complementary tasks: one is reserved specifically for specialist applications, including low dose microscopy, cryo-EM and tomography, while the other is used for routine microscopy. This division of labor avoids any compromise to the functioning of the specialist microscope, where optimal optical, vacuum and mechanical performance are crucial. Equipping both microscopes with slow scan CCD cameras will extend the advantages of this technology to all researchers who require it. A third TEM will continue to operate with film for researchers who prefer this medium.